Pump sucker rods in oil wells operate under severe conditions of load, abrasion and environment. They are subject to fatigue failure, corrosion, wear failure, etc., and these problems have been studied for many years, and numerous improved solutions have been proposed to the problem of optimum sucker rod structure, function and design. Durability and lightness are important features to be achieved. Typical of the approaches followed by the prior art are those disclosed in U.S. Pat. No. 4,205,926, issued June 3, 1980 (Carlson), and other prior art approaches, patents and publications mentioned therein, all of which are incorporated herein by reference.
The instant invention proposes a construction which may be of relatively light weight through the use of high carbon steel strand possessing at least approximately twice the tensile strength of most currently used rods, and in which fatigue failure of the strand is avoided or at least minimized. Sucker rods necessarily come in sections formed with end pieces or fittings for connection with other sections in assembling a sucker rod string of the requisite length. While there are advantages in using wire, strand, cable, wire rope, etc. as the major component of a sucker rod section, there has been and continues to be a definite problem of fatigue failure of the wire or the like in the area of its connection with an end piece or fitting. It is believed that this problem of fatigue failure is solved by the instant invention. The invention also proposes a construction which utilizes multi-wire, high carbon steel strand, which is lighter and stronger than materials known to me to be currently used in sucker rods, while minimizing problems of corrosion to which all strand is susceptible. The use of this lighter and stronger rod results not only in reduced pumping power cost, but also permits the use of lighter, less costly pumping units for wells of any given depth, thus reducing the capital investment. The increased strength also permits use of a lesser diameter rod, which facilitates overwrap with a protective material without increasing the diameter excessively. Such high carbon strand, because of its high strength and modulus of elasticity, also avoids problems of stretch which occur in many currently used rods. Finally, the invention proposes a construction utilizing a particularly advantageous strand, that is, low-relaxation strand, one version of which is well known for use in prestressed concrete, but which, to my knowledge, has never been used or proposed to be used in oil well sucker rods. Such low-relaxation strand has practically no creep, is highly resistant to fatigue failure, and, in common with other high carbon steels, is resistant to abrasion. While the invention finds particular utility in oil well sucker rods, it is not necessarily so limited, since there are various other uses for the invention.
Although the invention itself is as defined in the appended claims, the various features, advantages and objects of the invention will be best understood from the ensuing description of preferred exemplary embodiments, taken in conjunction with the accompanying drawings, which form a part of the instant specification and are to be read in conjunction therewith.